Elucidation of Ce/Zr Ratio Effects on the Physical Properties and Catalytic Performance of CexZr1-XO2 Catalysts

Cerium oxide (CeO₂) is widely used as a catalyst support because of its oxygen storage capacity (OSC) and Ce⁴⁺ and Ce³⁺ redox cycle, which helps avoid catalyst deactivation, such as coke formation. In addition to its structural attributes, cerium is one of the few rare earth metals that is affordable to purchase in bulk (about $6 USD/kg), making them appealing for many industrial applications such as steam reforming, preferential CO oxidation (PROX), and emission control. However, cerium oxide’s limitations include its low thermal stability and low density of defect sites on its surface. To combat this problem many researchers have incorporated different foreign metals such as zirconium, tin, titanium, and lanthanum to modify parts of the cerium oxide structure. In previous studies, the addition of zirconium, Ce_xZr_1-xO_y, shows a relatively better performance of the catalyst support in improving thermal stability and forming defect sites as compared to the addition of other metals. These supports can then be incorporated with various transition metals surface species for use in a wide range of industrial processes.

During this study, we investigated the effect of Ce:Zr ratio on the physical properties of a series of Ce_xZr_1-xO₂ catalysts, where x=1, 0.9, 0.6, 0.5, and 0. The UV and visible Raman spectroscopy, X-ray diffraction (XRD) spectroscopy, and thermogravimetric analysis (TGA) were applied to evaluate the defect sites, crystallite size, lattice parameters, and thermal stability of catalysts. With the collaboration with catalyst provider, DAICHI, reproducibility of tested catalysts was confirmed in addition to the surface area measurement data. As a model chemical reaction, CO oxidation was used to test the activity of the different catalysts as well as to describe the relationship between the structure and catalytic performance. Based on the characterization results, it is concluded that Ce_xZr_1-xO_y could be as a potential support for transition metals, including nickel, cobalt, copper, and so forth. The availability of commercially available Ce_xZr_1-xO_y catalyst supports make them a feasible choice for varying industrial processes.